Obsolescence is defined as the "transition from available to unavailable from the manufacturer in accordance with the original specification.
Many older technologies co-exist with newer alternatives, or are still in use due to cost, convenience, personal preference or availability.
Specialist or niche applications use technology that may have become commercially obsolete, like the vacuum tube.
Most experimental creations and conceptions, particularly in early development of technologies, like that of steam power, have also never been recorded.
Also not included are spurious inventions - technologies which are generally considered to not possess their claimed capabilities, to be hoaxes, or to not have ever existed in the first place.